ML15112B015

Primary Coolant Sys Pressure Isolation Valves,Oconee Units 1,2 & 3, Revised Technical Evaluation Rept

ML15112B015
Person / Time
Site:	Oconee
Issue date:	10/24/1980
From:	Noell P, Stilwell T FRANKLIN INSTITUTE
To:	Polk P Office of Nuclear Reactor Regulation
Shared Package
ML15112B014	List: ML15112B013 ML15112B015 ML15112B016
References
TER-C5257-218, TER-C5257-218-219-20, NUDOCS 8104270256
Download: ML15112B015 (8)

Text

THIS REPORT SUPERSEDES ISSUE OF AUGUST 22, 1980 TECHNICAL EVALUATION REPORT PRIMARY COOLANT SYSTEM PRESSURE ISOLATION VALVES DUKE POWER COMPANY OCONEE UNITS 1, 2., AND 3 NRC DOCKET NO.

50-269, 50-270, 50-287 NRCTAC NO.

12884, 12885, 12886 FRC PROJECT C5257 NRC CONTRACT NO. NRC-03-79-118 FRC TASK 218, 219, 220 Prepared by Franklin Research Center Author:

P. N. Noell The Parkway at Twentieth Street T. C. Stilwell Philadelphia, PA 19103 FRC Group Leader:

P. N. Noell Prepared for Nuclear Regulatory Commission Washington, D.C. 20555 Lead NRC Engineer: P. J. Polk October 24, 1980 This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, or any of their employees, makes any warranty, expressed or implied, or assumes any legal liability or responsibility for any third party's use, or the results of such use, of any information, apparatus, product or process disclosed in this report, or represents that its use by such third party would not infringe privately owned rights.

Franklin Research Center A Division of The Franklin Institute The Benjamin Franklin Parkway. Phila., Pa. 19103 (215) 48-1000 810427 0

1.0 INTRODUCTION

The NRC has determined that certain isolation valve configurations in systems connecting the high-pressure Primary Coolant System (PCS).to lower pressure systems extending.outside containment are potentially significant contributors to an intersystem loss-of-coolant accident (LOCA). Such configu rations have been found to represent a significant factor in the risk computed for core melt accidents.

The sequence of events leading to the core melt is initiated by the con current failure of two in-series check valves to function as a pressure isola tion barrier between the high-pressure PCS and a lower-pressure system extend ing beyond containment. This failure can cause an overpressurization and rup ture of the low-pressure system, resulting in a LOCA that bypasses containment.

The NRC has determined that the probability of failure of these check valves as a pressure isolation barrier can be significantly reduced if the pressure at each valve is continuously monitored, or if each valve is periodi cally inspected by leakage testing, ultrasonic examination, or radiographic inspection. The NRC has established a program to provide increased assurance that such multiple isolation barriers are in place in all operating Light Water Reactor plants designated by DOR Generic Implementation Activity B-45.

In a generic letter of February 23, 1980, the NRC requested all licensees to identify the following valve configurations which may exist in any of their plant systems communicating with the PCS: 1) two check valves in series or 2) two check valves in series with a motor-operated valve (MOV).

For plants in which valve configurations of concern are found to exist, licensees were further requested to indicate: 1) whether, to ensure integrity of the various pressure isolation check valves, continuous surveillance or periodic testing was currently being conducted, 2) whether any check valves of concern were known to lack integrity, and 3) whether plant procedures should be revised or plant modifications be made to increase reliability.

Franklin Research Center (FRC) was requested by the NRC to provide tech nical assistance to NRC's B-45 activity by reviewing each licensee's submittal

against criteria provided by the NRC and by verifying the licensee's reported findings from plant system drawings. This report documents FRC's technical review.

2.0 CRITERIA 2.1 Identification Criteria For a piping system to have a valve configuration of concern, the follow ing five items must be fulfilled:

1) The high-pressure system must be connected to the Primary Coolant System;

2) there must be a high-pressure/low-pressure interface present in the line;

3) this same piping must eventually lead outside containment;

4) the line must have one of the valve configurations shown in Figure 1; and

5) the pipe line must have a diameter greater than 1 inch.

MP j

LP Figure 1. Valve Configurations Designated by the NRC To Be Included in This Technical Evaluation 2.2 Periodic Testing Criteria For licensees whose plants have valve configurations of concern and choose to institute periodic valve leakage testing, the NRC has established criteria for frequency of testing, test conditions, and acceptable leakage rates.

These criteria may be summarized as follows:

2.2.1 Frequency of Testing Periodic hydrostatic leakage testing* on each check valve shall be accom plished every time the plant is placed in the cold shutdown condition for refueling, each time the plant is placed in a cold shutdown condition for 72 hours8.333333e-4 days <br />0.02 hours <br />1.190476e-4 weeks <br />2.7396e-5 months <br /> if testing has not been accomplished in.the preceding 9 months, each time any check valve may have moved from the fully closed position (i.e., any time the differen-tial pressure across the valve is less than 100 psig), and prior to returning the valve to service after maintenance, repair, or replacement work is performed.

2.2.2. Hydrostatic Pressure Criteria Leakage tests involving pressure differentials lower than function pres sure differentials are permitted in those types of valves in which service pressure will tend to diminish the overall leakage channel opening, as by pressing the disk into or onto the seat with greater force. Gate valves, check valves, and globe-type valves, having function pressure differential applied over the seat, are examples of valve applications satisfying this requirement. When leakage tests are made in such cases using pressures lower than function maximum pressure differential, the observed leakage shall be adjusted to function maximum pressure differential value. This adjustment shall be made by calculation appropriate to the test media and the ratio between test and function pressure differential, assuming leak age to be directly proportional to the pressure differential to the one half power.

2.2.3 Acceptable Leakage Rates:

• Leakage rates less than or equal to 1.0 gpm are considered accept able.

w Leakage rates greater than 1.0 gpm but less than or equal to 5.0 gpm are considered acceptable.if the latest measured rate has not exceeded the rate determined by the previous test by an amount To satisfy ALARA requirements, leakage may be measured indirectly (as from the performance of pressure indicators) if accomplished in accordance with approved procedures and supported by computations showing that the method is capable of demonstrating valve compliance with the leakage criteria.

that reduces the margin between measured leakage rate and the maximum permissible rate of 5.0 gpm by 50% or greater.

• Leakage rates greater than 1.0 gpm but less than or equal to 5.0 gpm are considered unacceptable if the latest measured rate ex ceeded the rate determined by the previous test by an amount that reduces the margin between measured leakage rate and the maximum permissible rate of 5.0 gpm by 50% or greater.

• Leakage rates greater than 5.0 gpm are considered unacceptable.

3.0 TECHNICAL EVALUATION

3.1 Licensee's Response to the Generic Letter In response to the NRC's generic letter [Ref. 11, the Duke Power Company (DPC) described in Reference 2 the valve configuration of concern as having two check valves in series with a single, normally closed, motor-operated valve (MOV.)

In a supplemental response, dated April 11, 1980, to the same NRC generic letter [Ref. 11, DPC futher explained the existing valve arrangement of concern:

"As stated in our previous response, the low pressure portion of each low pressure injection line at Oconee is isolated from the Reactor Coolant System (RCS) by two check valves inside containment and a normally-closed motor operated valve (MOV) outside containment. The break between high and low pressure piping occurs at the MOV."

The Licensee also indicated in this April 11, 1980 response that "Neither continuous surveillance nor periodic testing is being accomplished currently.

However, the check valves in question have exhibited no lack of integrity."

It is FRC's understanding that, with DPC's concurrence, the NRC will di rect DPC to change its Plant Technical Specifications as necessary to ensure that periodic leakage testing (or equivalent testing) is conducted in accor dance with the criteria of Section 2.2.

3.2 FRC Review of Licensee's Response FRC has-reviewed the licensee's response against the plant-specific Piping and Instrumentation Diagrams (P&IDs) [Ref. 3] that might have the valve con figurations of concern.

FRC has also reviewed the efficacy of instituting periodic testing for the check valves involved in this particular application with respect to the re duction of the probability of an intersystem LOCA in the Low-Pressure Injec tion pipe lines.

In its review of the P&IDs [Ref. 3] for Oconee Units 1, 2, and 3, FRC found the following piping system to be of concern:

The Low-Pressure Injection System (LPIS) for Oconee Units 1, 2, and 3 is composed of two piping branches (A and B), both leading directly into the reactor vessel. As described previously by the licensee, each branch has two check valves and a motor-operated valve, normally closed (n.c.), in one of the series configurations of concern with the high-pressure/low-pressure interface on the upstream side of the single MOV. The valves involved in this dis cussion are listed below for Oconee Units 1, 2, and 3:

Low-Pressure Injection System Unit I Branch A Branch B high-pressure check valve CF-12 CF-14 high-pressure check valve LP-47 LP-48 high-pressure MOV, n.c.

LP-18 LP-17 Unit 2 high-pressure check valve 2CP-12 2CP-14 high-pressure check valve 2LP-47 2LP-48 high-pressure MOV, n.c.

2LP-18 2LP-17 Unit 3 high-pressure check valve 3CP-12 3CF-14 high-pressure check valve 3LP-47 3LP-48 high-pressure MOV, n.c.

3LP-18 3LP-17 In accordance with the criteria of Section 2.0, FRC found no other valve configurations of concern existing in this plant. These findings confirm the licensee's response [Ref. 21.

FRC reviewed the effectiveness of instituting periodic leakage testing of the check valves in these lines as a means of reducing the probability of an intersystem LOCA occurring. FRC found that introducing a program of check valve leakage testing in accordance with the criteria summarized in Section 2.0 will be an effective measure in substantially reducing the probability of an intersystem LOCA occurring in these lines and a means of increasing the probability that these lines will be able to perform their safety-related functions. It is also a step toward achieving a corresponding reduction in the plant probability of an intersystem LOCA in Oconee Units 1, 2 and 3.

4.0 CONCLUSION

Oconee Units 1, 2, and 3 have been determined to have valves in one of the configurations of concern in both branches of each respective Unit Low Pressure Injection System.

If DPC modifies the Plant Technical Specification for Oconee Units 1, 2, and 3 to incorporate periodic testing (as delineated in Section 2.2) for the check valves itemized in Table 1.0, then FRC considers this an acceptable means of achieving plant compliance with the NRC staff objectives of Reference 1.

Table 1.0 Primary Coolant System Pressure Isolation Valves System Check Valve No.

Allowable Leakage*

Low-Pressure Injection Unit 1 Branch A CF-12 LP-47 Branch B CF-14 LP-48 Unit 2 Branch A 2CF-12 2LP-47

• To be provided by licensee at a future date in accordance with Section 2.2.3.

Branch B 2CF-14 2CF-48 Unit 3 Branch A 3CF-12 3LP-47 Branch B 3CF-14 3LP-48

5.0 REFERENCES

[1[. Generic NRC letter, dated 2/23/80, from Mr.

D. G. Eisenhut, Department of Operating Reactors (DOR), to Mr. W. 0. Parker, Jr., Duke Power Company (DPC).

[2].

Duke Power Company's response to NRC's letter, dated 3/13/80, from Mr.

W. 0. Parker, Jr., (DPC) to Mr. D. G. Eisenhut (DOR).

[3].

List of examined P&IDs:

Duke Power Company's Drawings of Ocouee Units 1, 2, and 3:

PO-100A-1, (Rev. 18)

PO-IOOA-2, (Rev. 15)

PO-1OOA-3, (Rev. 16)

PO-101-A-1, (Rev. 21)

PO-101-A-2, (Rev. 14)

PO-101-A-3, (Rev. 14)

PO-102A-1, (Rev. 34)

PO-102A-2, (Rev. 20)

PO-102A-3, (Rev. 24)

PO-101B-1, (Rev. 25)

PO-101B-2, (Rev.

24)

PO-101B-3, (Rev.

24)

PO-110A-1, (Rev.

29)

PO-11OA-3, (Rev. 18)

PO-120A, (Rev. 12)